Gradual demise of a thin southern Laurentide ice sheet recorded by Mississippi drainage
Gradual demise of a thin southern Laurentide ice sheet recorded by Mississippi drainage
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密西西比河排水系统记录的南劳伦太德冰盖逐渐消亡
DOI：
10.1038/nature12609
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发表时间：
2013
期刊：
影响因子：
64.8
通讯作者：
R. Anderson
中科院分区：
文献类型：
--
作者：
A. Wickert;J. Mitrovica;Carlie Williams;R. Anderson
在末次盛冰期（LGM），即距今约 21,000 年前，陆地冰盖所储存的水足以使全球平均海平面降低 130 米。然而，经过几十年的研究，冰的分布仍然存在重大不确定性。在这里，我们使用水混合模型将北美冰消冰盖历史的四个重建与来自墨西哥湾的高分辨率氧同位素 (δ18O) 记录定量连接起来。对于每次重建，我们都会将融水和季节性径流输送到随时间演变的密西西比流域，该盆地与冰的几何形状和不断变化的地形共同演变，因为冰载荷使固体地球变形，并在称为冰川均衡调整的过程中产生空间变化的海平面。 δ18O记录显示，密西西比州排干的劳伦太德冰盖南部仅对全球海平面上升贡献了5.4±2.1米，其中0.66±0.07米是在距今14,650-14,310年前的融水脉冲1A事件中释放的，远少于之前认为的水量。相比之下，基于冰川均衡调整的三种重建结果高估了基于 δ18O 的末次盛冰期后融水量 1.6 至 3.6 倍。第四次重建基于冰物理学，具有足够低的密西西比航道融水排放量，与 δ18O 约束一致，但也包含北美最大的末次盛冰期冰量。这表明基于冰物理的建模可能是匹配同位素记录的最佳方法，同时还能在北美冰盖中封存足够的水以匹配观测到的末次盛冰期海平面下降。
At the Last Glacial Maximum (LGM), about 21,000 years before present, land-based ice sheets held enough water to reduce global mean sea level by 130 metres. Yet after decades of study, major uncertainties remain as to the distribution of that ice. Here we test four reconstructions of North American deglacial ice-sheet history by quantitatively connecting them to high-resolution oxygen isotope (δ18O) records from the Gulf of Mexico using a water mixing model. For each reconstruction, we route meltwater and seasonal runoff through the time-evolving Mississippi drainage basin, which co-evolves with ice geometry and changing topography as ice loads deform the solid Earth and produce spatially variable sea level in a process known as glacial isostatic adjustment. The δ18O records show that the Mississippi-drained southern Laurentide ice sheet contributed only 5.4 ± 2.1 metres to global sea level rise, of which 0.66 ± 0.07 metres were released during the meltwater pulse 1A event 14,650–14,310 years before present, far less water than previously thought. In contrast, the three reconstructions based on glacial isostatic adjustment overpredict the δ18O-based post-LGM meltwater volume by a factor of 1.6 to 3.6. The fourth reconstruction, which is based on ice physics, has a low enough Mississippi-routed meltwater discharge to be consistent with δ18O constraints, but also contains the largest LGM North American ice volume. This suggests that modelling based on ice physics may be the best way of matching isotopic records while also sequestering enough water in the North American ice sheets to match the observed LGM sea level fall.